The present invention relates to a safety switch.
Safety switches are well known, and are typically used to prevent access to for example electromechanical machinery when that machinery is in operation. In a conventional arrangement the safety switch is mounted on a doorpost of a machinery guard, and an actuator for the safety switch is mounted on a corresponding door. When the door is closed the actuator engages with the safety switch, which in turn closes a set of electrical contacts which allows power to be supplied to the machinery. This arrangement ensures that power can only be supplied to the machinery when the guard door is shut. When the guard door is opened, the actuator disengages from the safety switch, thereby opening the electrical contact and cutting off the supply of power to the machinery.
Some safety switches are provided with locking mechanisms which prevent the actuator from being removed from the safety switch until the locking mechanism has been deactivated. The locking mechanism can be deactivated by supplying the mechanism with an electrical signal, for example. A locking mechanism may be desirable when the machinery does not stop immediately after its power supply has been cut, or where premature interruption of the operation of the machinery could cause damage to parts of the machinery, or tools used by the machinery. A disengaging signal may not be sent to the locking mechanism until a predetermined time has passed after the power supply to the machinery has been cut-off.
It has been found that in some safety switches incorporating a locking mechanism, the locking mechanism can be temporarily disengaged by providing the safety switch with a sudden physical shock (e.g. suddenly moving or hitting the safety switch). When the locking mechanism is temporarily disengaged the actuator may be removed from the safety switch without a disengaging signal being sent to the locking mechanism. This means that a user can gain access to the machinery while it is still in motion, even though the power supply to the machinery has been cut-off, i.e. the time delayed unlocking of the locking mechanism is circumvented.
It is thus desired to overcome or substantially mitigate the above disadvantage.